Red Maple Earns Its Popularity
The red maple, Acer rubrum, is one of the most popular and widely used trees in the home landscape, thriving in USDA Hardiness Zones 3 to 10. This medium-sized, deciduous tree is native to Eastern North America, ranging from Quebec to Minnesota, south to Florida, and west to eastern Texas. In the southernmost parts of their range, red maples are a wetland species, which has earned them the nickname “swamp maple.” Not all red maples turn red in the fall, which is why plant breeders have developed cultivars that offer more dependable, vibrant fall color. The term rubrum, of its Latin name, describes the overall redness of the tree, rather than fall foliage.
Clusters of small, red buds and red flowers appear on the tree in early spring (March/April) before the leaves appear. Male and female flowers typically occur on separate trees, but can be on separate branches on the same tree. Occasionally flowers are perfect (have both male and female parts). Male flowers are pink to red, rarely yellow; female flowers have two bright red arching styles in the center. The flowers become reddish-green, two-winged fruits (samaras) that can be seen twirling to the ground by early May. Twigs are reddish. Leaves are medium to dark green, 2–6″ in length, with 3 or 5 lobes, and roughly-toothed edges. Young trunks are smooth and light gray; older trunks are darker gray and separated by vertical ridges into large, plate-like scales.
IN THE WILD
Red maples are perhaps the most abundant tree in the eastern deciduous forest. This status can be attributed to the tree’s generalist tendencies. A generalist species is one that can tolerate a wide range of habitat conditions and uses many different types of resources. Red maples do well in sunny or shady spots, dry or wet soil, and high or low elevation. Adaptable roots help the red maple to cope with differing moisture levels. If the tree is placed in wet soil, it grows a short taproot and extensive lateral roots to soak up water at the surface. When red maples grow in dry sites, a long taproot and short lateral roots develop. Despite their remarkable adaptations, red maples grow better in some conditions than in others. Deep, moist, acidic soil results in the healthiest red maples.
Although their life span averages 80-100 years, not a long life in tree terms, they begin producing seeds at about 4 years. After fires or hurricanes, when many trees are decimated, red maples spring up quickly and can become the dominant species in the forest.
The fruits (samaras) provide food for squirrels and many other rodents. Young shoots are a favorite of white-tailed deer. Horse owners should note, however, that wilted or dried maple leaves can be toxic to horses. Doug Tallamy (2009) notes that in addition to the red maple acting as a larval host for the Cecropia Moth (Hyalophora cecropia), maples support many forest-loving Lepidoptera:
If you plant native maples in your yard, you are enabling the rosy maple moth (Dryocampa rubicunda), the oval-based prominent moth (Peridea basitriens), the retarded dagger moth (Acronicta rubicoma), the orange-humped maple worm (Symmerista leucitys), the maple looper (Parallelia bistriaris), and the Baltimore bomolocha (Bomolocha baltimoralis or Hypena baltimoralis) to exist where they otherwise could not.
The bark is thin on most maples, and easily damaged by mechanical impact. Wounds can make the tree more susceptible to disease and insects. To avoid damaging shallow feeding roots, trees should be planted where turf below the canopy is not desired. Mulching around trees will help protect the trunk and roots from mechanical damage, conserve moisture, and help keep soil temperatures cool. Spread mulch 2-4″ deep to the drip line of the tree canopy, making sure that the mulch does not touch the trunk, and that the root flare is visible. The mulch should form a flat “donut” with the tree’s trunk in the center. (See mulching guidelines provided by the Charlottesville Area Tree Stewards.)
Watch for aphids, leafhoppers, borers, scale and caterpillars. Leafhoppers can cause substantial damage. Canker, fungal leaf spot, and root rots may occur. Red maples are also subject to anthracnose fungus, but this is usually not serious. Verticillium wilt is a much bigger problem and is discussed below. Wind and ice may break some branches. Alkaline soils (those with a pH above 7.5) usually cause leaf chlorosis (a yellowing of the leaf blades, often with pronounced green veins). Abnormal yellow color in maple trees is frequently associated with nutrient deficiencies, particularly manganese. Manganese nutrient deficiency leads to nitrogen deficiency, resulting in poor chlorophyll production and stunted growth. As soil pH increases (becomes more alkaline), the ability of the red maple to take up manganese decreases. If high pH is verified by a soil test, you can lower your soil’s pH (make it more acidic), by applying elemental sulfur or acidifying fertilizers.
Red maple is somewhat sensitive to being transplanted in autumn, and care should be taken to amend the soil, fertilize, water thoroughly, mulch adequately, and avoid winter salt spray, to enhance survival chances during the first winter. Maples are considered ‘bleeders’ and are best pruned in early winter or during summer. They do not tolerate heavy pollution.
Maples are susceptible to Verticillium wilt which attacks the vascular system and can be fatal. Verticillium wilt is caused by a soil fungus called Verticillium dahliae. This fungus lives in soil as small, darkened structures called microsclerotia. These microsclerotia may lie dormant in the soil for up to 10 years. When the roots of susceptible plants grow close to the microsclerotia, the fungus germinates and infects the roots of the plants through wounds or natural openings. The fungus spreads into the branches through the plant’s vascular system and simultaneously causes the plant cells to “plug” themselves. Once the xylem is infected, it becomes so plugged that water can no longer reach the leaves. Verticillium can spread through wounds on branches or trunks.
The disease can occur either acutely or chronically. In acute infections, a branch or a section of several branches of the tree may wilt and turn brown rather suddenly. Often, other branches soon follow, until most or all of the branches are wilted. Leaves may also turn yellow between the veins, or may drop prematurely. Branches may die back. Acute infections occur when the fungus is living in the newest wood (the sapwood).
In chronic infections, leaves may be smaller than usual or yellow, often with brown edges. The tree may grow poorly and may produce abnormally large seed crops. The tree does not wilt or die quickly, but declines slowly over time. Chronic infections occur when the fungus is living in older wood. The appearance of streaking helps to identify the disease but does not guarantee that the tree has Verticillium wilt. Sometimes other factors or diseases cause discoloration of sapwood. Only laboratory examination can positively diagnose the disease. At this time, there is no known chemical control for this disease.
Because the fungus lives in the soil and does not spread through the wind, there is no need to quickly remove infected trees. Dead branches should be pruned out to prevent infection by other fungi; remember to sterilize tools. Plants showing early symptoms should be watered and fertilized. Use fertilizers lower in nitrogen and higher in potassium. When replacing trees that have died from Verticillium wilt, choose resistant species such as conifers, crabapple, beech, ginkgo, hackberry, hawthorn, hickory, white oak and poplar, among others. Visit this link for a listing of trees and shrubs that are susceptible to the disease. Allow several years (three or more) before growing a susceptible plant in an infected area. Do not plant back into the same hole.
ACER RUBRUM CULTIVARS
Acer rubrum is prized for its adaptability to different conditions, its fast growth rate, pleasing form, and fall color. Consistently beautiful fall color, however, is available through cultivars.
The following lists includes some of the more frequently used red maple cultivars, so that readers interested in planting a red maple can learn about the characteristics of different cultivars. These lists might also help clear up some of the confusion between cultivars that are crosses between red maples, and cultivars that are crosses between red maples and silver maples. This first list shows cultivars that are crosses between red maples.
Acer rubrum ‘October Glory’: This female cultivar (patented in 1961) grows 40-60’ tall and 20-25’ wide with an oval rounded form. Attractive red flowers appear in early spring before the foliage emerges. Flowers give way to red-tinged samaras. Glossy dark green leaves retain good green color well into fall (longer than many other A. rubrum cultivars), and in more northern areas are sometimes subjected to frost prior to acquiring fall color. It is best used north of USDA hardiness zone 9. Orange to red fall color for this cultivar is brilliant in most years. It turns color late in October.
Acer rubrum ‘Autumn Flame’: Patented in 1964, this male selection produces greenish-yellow flowers in spring, but no fruit. It is noted for abundant leaves that are smaller in size than those of the species. A brilliant scarlet fall color develops about two weeks prior to fall color on the species. Noted for its pleasing rounded habit as a young tree, it matures 40-60′ tall, and 30-50’ wide. May lack the hardiness of other cultivars.
Acer rubrum ‘Brandywine’: A cross between two popular red maple cultivars, ‘October Glory’ and ‘Autumn Flame’. It grows 40’ tall and 30’ wide; oval form; male cultivar (seedless); deep red fall color; resistant to leafhopper.
Red Sunset® red maple (Acer rubrum ‘Franksred’): Grows 40-50’ tall and 30-35’ wide; pyramidal to rounded form. In early spring before the leaves emerge, tiny red flowers cover the canopy of the tree. The samaras, or winged seeds, turn bright red in early summer and then fade to brown and fall to the ground. Foliage starts as a glossy, dark green turning to bright reds and oranges in the fall. One of the best red maples for fall color.
Redpointe® red maple (Acer rubrum ‘Frank Jr.’): A pyramidal shape growing 40-50’ tall and 25-30’ wide. Foliage starts as a bright green in spring, darkening to a glossy, dark green in summer, and turning to a brilliant red in the fall. It has a high canopy with a typical clearance of 6 feet from the ground, and should not be planted underneath power lines. As it matures, the lower branches of this tree can be strategically removed to create a high enough canopy to support unobstructed human traffic underneath.
Acer rubrum ‘Bowhall’ – Growing to 45’ tall and 15’ wide, it is narrower in width than other red maple cultivars, such as ‘Red Sunset’ or ‘October Glory’, making it suitable to smaller planting areas. Leaves are borne on upright stems which give the tree its upright to oval crown at maturity. During the summer months, the leaves are dark green above and grayish beneath. In the fall, the leaves turn shades of yellow, orange and reddish-orange. It is considered to have better fall color than the Freeman maple cultivar ‘Armstrong’.
Two newer cultivars have been introduced from the U.S. National Arboretum red maple research project. Both are male cultivars that don’t produce seed, show good leafhopper resistance, and exhibit brilliant red fall color. As new introductions, they don’t seem to be widely available at this point. Both prefer full sun and moist, acidic soils.
Acer rubrum ‘Somerset’: A cross between A. rubrum ‘October Glory’ and A. rubrum ‘Autumn Flame’. Grows 40’ tall and 30’ wide. Showy clusters of red flowers in early spring; foliage emerges red in the spring, turning to medium green. Strong, upright growth habitat with a moderately ovate crown. Bark is silvery gray and furrowed. Long-lasting brilliant red color starts in late October; has been shown to color well as far south as Georgia (Hardiness zone 8).
Acer rubrum ‘Sun Valley’: A cross between A. rubrum ‘Red Sunset’ and A. rubrum ‘Autumn Flame’. Grows to 40’ tall and 35’ wide; oval and densely branched. It has pink, ball-shaped flowers in spring. Bark is light gray and smooth when young, turning dark gray with age. USDA Hardiness zones 4-7.
FREEMAN MAPLE (ACER FREEMANII)
Freeman maples are hybrids of red maples and silver maples. They combine the strong branch attachment of the red maple and the fast growth rate of the silver maple. One criticism cited is a tendency for these cultivars to develop multiple leaders that, in combination with narrow crotch angles, may predispose the tree to structural failure later in life. These cultivars have a brilliant, red-orange color in the fall, and are less prone to chlorosis symptoms due to alkaline soils. Oliver M. Freeman of the National Arboretum made the first controlled crosses between red maple and silver maple in 1933. Crosses between red and silver maples occur not only by controlled propagation, but also naturally in the wild. It is sometimes difficult to identify a Freeman hybrid because of the complexity of crosses and backcrosses that may occur. Cultivars are sometimes listed for sale by nurseries under Acer rubrum instead of Acer × freemanii, making it difficult for consumers to know what they’re buying. To understand these cultivars, let’s look at the characteristics of the silver maple.
SILVER MAPLE (ACER SACCHARINUM)
The silver maple is native to the eastern and central United States and to Canada. This is the fastest growing of all American maple species, with a growth rate of 10-12’ in four to five years. It grows 50-70’ tall and 35-50’ wide. Although it tolerates a wide variety of soils, it prefers moist soils in deep woods and along stream banks. This tree has a very vigorous root system that can buckle sidewalks, clog drain tiles, and invade septic fields or well pipes. Due to its rapid growth, the wood is weak and prone to storm damage. It is susceptible to many diseases and insect pests, particularly the woolly alder aphid.
In spite of these problems, silver maple is a very popular tree and planted often, mainly because of its rapid growth and ease of culture. The bright green leaves are silvery underneath, and are especially attractive when fluttering in the wind.
ACER x FREEMANII CULTIVARS
Armstrong Freeman maple (Acer x freemanii ‘Armstrong’): With an upright, narrow form, this tree can reach a height of 50-70’ with a 15-20’ spread. It can tolerate wet soils. Although it does not have strong fall coloration, it does turn orange-red. Other cultivars are considered to have better fall color.
Armstrong Gold red maple (Acer rubrum ‘KW78’ ): Selected from an evaluation of hundreds of seedlings of ‘Armstrong’, this cultivar improves greatly on the parent, with brighter foliage color, greater foliage density, and a compact, less leggy growth habit. Its columnar form recommends it for narrow street planting sites. Grows 40’ tall and 12’ wide.
Autumn Blaze® Freeman maple (Acer x freemanii ‘Jeffsred’): A rounded to broad oval tree, growing 50-60’ tall and 40-50’ wide. It has a strong central leader and better branching habit than silver maple, making it better adapted to areas with either ice or snow. Fall color is a consistent orange-red to scarlet-red. Originally thought to be a male tree, it has produced fruit in some cases. It tolerates clay soil, and will withstand both wet soil conditions and drought.
Autumn Fantasy® Freeman maple (Acer x freemanii ‘DTR 102): A broadly oval form growing about 50’ tall and 40’ wide. Produces bright red fall color. This maple is drought tolerant.
Celebration® Freeman maple (Acer x freemanii ‘Celzam’): A broadly oval form growing about 50’ tall and 35’ wide. Leaves are similar to silver maple, but this cultivar has a more uniform growth habit, making it more resistant to storm damage. It is more tolerant of urban conditions. Fall color is yellow to orange.
Firefall™ Freeman maple (Acer x freemanii ‘AF#1’): An upright, oval form growing 50’ tall and 35’ wide. The orange-red-to-red fall color develops a little earlier than other cultivars. Better suited to northern climates.
Marmo (Acer x freemanii ‘Marmo’): This cultivar has a uniform, upright-to-columnar form. It grows 45-70’ tall and 40’ wide. It has a strong central leader and excellent branching habit. Fall color is an interesting mottled blend of red and green to burgundy and yellow. Produces no fruit. The parent tree was selected from the collections at The Morton Arboretum and is a Chicagoland Grows® introduction. (See this link for information on Chicagoland Grows®.)
Sienna Glen® Freeman maple (Acer x freemanii ‘Sienna’): This cultivar has a strong central leader and a uniform, pyramidal shape, making it less prone to breaking in wind and storms. It grows 50’tall and 35’ wide. Fall color is orange to red-burgundy. This is an excellent street or specimen tree and is tolerant of salt, drought, flooding, alkaline soils, and pollution.
If you are looking for a native shade tree that can thrive in many different conditions, the red maple steps to the front. It is happiest in full sun and in acidic, moist-to-wet soils. Cultivars offer consistently beautiful fall colors that help ease the pain of saying goodbye to summer. Freeman maples are a cross between red maples and silver maples. These cultivars were developed to combine the very fast growth rate of the silver maple, and the stronger form of the red maple. There is still some concern about its predisposition to structural failure later in life, particularly if planted in high wind areas. Freeman cultivars are generally more tolerant of alkaline soils than are red maples. As native trees, red maples are important contributors to a diverse ecosystem of native plants, insects, and birds that support each other robustly and thrive in our home landscapes.
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Featured photo: Acer rubrum (Swamp Maple) Photo: Chris Evans, University of Illinois, Bugwood.org